1. Field of the Invention
The present invention relates to a deformable mirror device (DMD) for changing a proceeding path of an incident light, and more particularly, to a deformable mirror device having an improved structure so that the path of light can be easily changed with a low driving voltage.
2. Description of the Related Art
In general, DMDs having a plurality of reflection mirrors installed to be capable of pivoting by an electrostatic force are for changing a path of light by a predetermined degree. The DMD is used in image display devices of a projection TV, and optical scanning devices such as a scanner, copying machines, and facsimile machines. In particular, when being adopted as an image display device, as many reflection mirrors as the number of pixels are arrayed on a two dimensional plane and each reflection mirror is pivoted according to video signals to each pixel to adjust color and brightness.
Referring to FIG. 1, a conventional DMD is comprised of a substrate 1, a pair of posts 3 protruding from a surface of the substrate 1 and spaced apart a predetermined distance, an electrode 5 formed on the substrate 1, and a reflection mirror 7 supported by the posts 3 and arranged to face the electrode 5. The reflection mirror 7 has a pair of support pieces 9 extending therefrom and connected to the posts 3 for supporting the reflection mirror 7.
As shown in the drawing, the support pieces 9 are formed to be asymmetrical such that one support piece 9a is shorter than the other support piece 9b, i.e., L1.noteq.L2 and is elastic enough to support the reflection mirror 7. However, the support piece 9 may have a symmetrical structure.
The electrode 5 has a size corresponding to the reflection mirror 7 and is installed on the substrate 1 to face the reflection mirror 7. Thus, when an electrical potential is applied to the electrode 5, an electrostatic attraction force is generated by the electrical potential difference between the electrode 5 and the reflection mirror 7 and thus the reflection mirror 7 approaches toward the electrode 5 overcoming the rigidity of the support piece 9, thereby changing its inclination. When the electrical potential difference between the electrode 5 and the reflection mirror 7 disappears, the reflection mirror 7 returns to its original state due to the rigidity of the support piece 9 and maintains a horizontal state.
In the DMD having the above asymmetrical structure, as shown in FIG. 2, when an electrical potential difference is generated between the electrode 5 and the reflection mirror 7, the boundary portions between the support pieces 9a and 9b and the reflection mirror 7 respectively receive forces F.sub.1 and F.sub.2 directing the electrode 5. Accordingly, the reflection mirror 7 sags downward a predetermined distance (d.sub.1 and d.sub.2). Here, the forces F.sub.1 and F.sub.2 differ from each other by the difference in the rigidities k.sub.1, and k.sub.2 of the two support pieces 9a and 9b, and the distances d.sub.1 and d.sub.2 indicating the displacement of the reflection mirror 7 downward also differ from each other, so that the inclination of the reflection mirror 7 is determined.
The forces F.sub.1 and F.sub.2 are inversely proportional to the distances L.sub.1 and L.sub.2 between the resultant force F.sub.es of a point from which the electrostatic attraction force acts and the support point of the post 3.
In the drawing, since L.sub.1 &lt;L.sub.2 and k.sub.1 &gt;k.sub.2, and F.sub.1 &gt;F.sub.2, the larger force F.sub.1 is applied to the portion with a larger rigidity k.sub.1, and the smaller force F.sub.2 is applied to the portion with a smaller rigidity k.sub.2. Thus, the inclination becomes less. Meanwhile, increases of voltage applied to the electrode 5 and stress acting on the support piece 9 may cause the product to be less reliable.
Further, as shown in FIG. 3, when the two support pieces 9 are arranged to be symmetric (L.sub.1 =L.sub.2), since the forces F.sub.1 and F.sub.2 and the rigidity k.sub.1, and k.sub.2 of the support piece 9 are equal, the reflection mirror 7 sags toward the electrode 5 while maintaining a horizontal state. Thus, no change in the light path occurs.